An implantable cardiac device is a medical device that is implanted in a patient to monitor electrical activity of a heart and to deliver appropriate electrical. Implantable cardiac devices include, for example, pacemakers, cardioverters, defibrillators, and the like. The term “implantable cardioverter defibrillator” or simply “ICD” is used hereinafter to refer to any implantable cardiac device.
An ICD employs a battery to power its internal circuitry and to generate electrical therapy for delivery to the patient. The electrical therapy can include any one of pacing pulses, cardioversion pulses or defibrillation pulses. In addition to providing electrical therapy, the ICD generates information related to device operation, patient therapy and patient status. Such information is typically provided to the patient's care provider using a telemetry circuit that communicates with a nearby, short-range external system, such as a device programmer. In conventional ICDs, a single power source provides the power necessary to operate internal circuitry, generate electrical therapy and transmit information.
Communication between ICDs and more remote, long-range external devices is also desirable. Unfortunately, long-range telemetry systems require substantially more power than short-range system, and accordingly may reduce the lifetime of a typical ICD battery. A substantial decrease in battery life is undesirable in that device replacement may be required at an earlier stage.